Z8 Tires Sizes, Wheel Offsets and Weights

[macfly]

The wheel offsets for the Z8 are 20mm front, 22mm rear.

Here is a list of tire sizes suitable for BMW Z8.

Front stock tire size:
245/45/18 339mm in radius
Front upgrade tire size:
255/40/18 331mm
245/40/19 339mm
255/35/19 331mm
265/40/19 - GM
245/35/20 340mm
255/35/20 343mm

Rear stock tire size:
275/40/18 339mm in radius
Rear upgrade tire size:
285/40/18 343mm
295/35/18 332mm
275/35/19 338mm
285/35/19 341mm
295/30/19 330mm
285/30/20 340mm

The chart suggests that the best front and rear combination is 245/40/19 front / 275/35/19 or 285/35/19 rear in 19", however GM has been running 265/40/19 - 285/35/19 and is very keen on that combo as the wider front footprint gives increased grip and neutralizes understeer.


This is a weight comparison chart for some of the common tire/wheel combos

wheel...................tires...............................front............................................rear

Stock.....................Bridgestone RE040r/f........62lbs/28.1k - 245/45/18..................67lbs/30.4k - 275/40/18
rims alone..............18 x 8 / 18 x 9................29lbs/13.1k...................................31lbs/14.1k


BBS RGR 19"...........Michelin PS2....................46lbs/20.8k - 265/35/19..................50lbs/19.5k - 285/35/19

BBS RGR 19"...........Yokohama Advan Sport.....49lbs/22.2k - 265/35/19..................53lbs/23.6k - 285/35/19

BMW Style 166 19"...Conti Sport Contact 2........53 lbs/24k - 255/40/19....................59.5 lbs/27k - 285/35/19
rims alone..............19 x 8.5 / 19 x 9.5............26lbs/11.8k...................................29 lbs/13.1k


BBS RS-GT 20"........Michelin PS2....................48lbs/21.8k - 255/40/19..................52lbs/23.6k - 285/35/19

Hamann 20"............Michelin PS2....................61lbs/27.7k - 255/35/20..................63lbs/28.6k - 285/30/20
rims alone..............20 x 9 / 20 x 10.5............31lbs/14.1k...................................36 lbs/16.3k

BMW M Sport 20".....Pielli P Zero.....................61lbs/27.7k - 255/35/20..................66lbs/30k - 295/30/20

Alpina Rims 20".......Michelin PS2.....................57.2 lbs/25.9k - 255/35/20..............58.7lbs/26.6k - 285/30/20
rims alone..............20 x 9 / 20 x 10................31.6lbs/14.3k................................32.5 lbs/16k

[Norcal]

STOCK:
F 18x8, 20mm offset, 120mm lug space, 30 lbs, 245/45/18
R 18x9, 22mm offset, 120mm lug space, 32 lbs, 275/40/18

ALPINA V8:
F 20x9, 20mm offset, 120mm lug space, ??lbs, 255/35/20
R 20x10, 22mm offset, 120mm lug space, ??lbs, 285/30/20

HARTGE WHEELS:
"Classic"
F 20x9 - 18mm offset
R 20x10 - 22mm offset
"Nova"
F 20x9 - 18mm offset
R 20x10 - 28mm offset (I don't understand why so much difference)

One owner (iGuZ8) has mounted on "Nova"
F 255/35/ZR20
R 305/25/ZR20

[macfly]

Wheel Offset: Distance from the center (half way between the inner edge and outer edge) of the rim to the mounting surface that contacts the rotor hub or drum.

If the center of the rim is located outboard of the mating surface, that's negative offset. If the center of the rim is located inboard of the mounting surface, that's positive offset. If the rim center is in-line with the mounting surface, that's zero offset. So, offset refers to the location of the wheel center, relative to the mounting surface.

Negative offset creates a wider track, moves the wheel/tire towards the lip of the fender and creates a deep dished look on the street side of the wheel. Positive offset creates a more narrow track, moves the wheel/tire inwards so they are closer to the brakes and suspension parts and creates a flatter street side appearance.

To measure wheel offset, you begin by measuring the wheel's backspacing. Lay the wheel face down, place a straight edge across the center of the upper edge of the rim (this is the wheel's inside edge), then measure the distance from the mounting surface to the bottom of the straight edge. This gives you the wheel's backspace. Now use the following formula to figure the wheel's offset: Backspace minus 1/2 wheel width = wheel offset. The number will be either positive, negative or zero, as described above.

Too much negative wheel offset can cause interference between the outer edge of the tire and fender lip, place undue stress on the wheel bearings, ball joints and control arms, and cause steering wheel kickback and increased steering effort. Too much positive wheel offset can cause interference problems between the wheels and the brake calipers, other suspension parts, or the inner fender wells. Your best bet is to stay as close to the factory offsets as possible.

If you increase the width of the rims, your new wheel offsets will no longer correspond to the factory offsets. For example, if you keep the same offsets as the original wheels but go to wider rims, you will add an equal amount of width inboard and outboard which may not be what you want. Careful measurements for clearance are critical. This is where recommendations from wheel manufacturers and/or places like The Tire Rack can be very helpful.

[Z8doc]

the Offset for the OEM Z8 18x8 / 18x9 is the same as the 20" Alpina wheels.

Z8
18x8 offset 20mm front 30lbs
18x9 offset 22mm rear 32lbs

Alpina V8 roadster
20x9 offset 20mm front 28lbs (?)
20x10 offset 22mm rear 30lbs (?)

So, with the offsets the same, the larger and lighter MPS PS2s will clear fine front and rear. Most brands other than BMW seem to have a 20mm offset for the front in both 19" and 20" rims but considerable variability in the offsets for the rear. It seems that a 22 - 25mm offset is what most recommend if you are going bigger in the rear. There seems to be enough clearance of the MPS PS2s with that offset.

[stuartsackley]

Do you know if 19x8 and 19x9 1/2 wheels off of a BMW 545,will fit on a Z8?
Thank you.

[macfly]

I think you could find that info from a BMW dealer. I can't help as I have no idea what any of the other measurements for those wheels are.

[Z8doc]

Which particular wheel as there are many available for the 545i and what particular year 545i are you referring too, the e60 or the e61? The M Cross Spoke 101 in the 8x19 front:et 20 and 9 1/2 x 19. et 32 might fit but this same wheel in the 20" version (9x20:et24 front and 10x20:et 24 rear) will fit for sure and can be found on Carlos' red/red Z8 here in the wheel forum -- they are stunning.

The stock offset of et:20 front and et:22 rear for the Z8's 18" wheels should be adhered to as close as possible as if you stray to far, you may need wheel hub centric spacers, which, theoretically, is not as secure as without the spacers.

[stuartsackley]

Which particular wheel as there are many available for the 545i and what particular year 545i are you referring too, the e60 or the e61? The M Cross Spoke 101 in the 8x19 front:et 20 and 9 1/2 x 19. et 32 might fit but this same wheel in the 20" version (9x20:et24 front and 10x20:et 24 rear) will fit for sure and can be found on Carlos' red/red Z8 here in the wheel forum -- they are stunning.

The stock offset of et:20 for the Z8's 18" wheels should be adhered to as close as possible as if you stray to far, you may need wheel hub centric spacers, which, theoretically, is not as secure as without the spacers.

thank you.

[macfly]

wheel with tire weights added to lead post - if anyone has weights of alternative wheel/tire combos let me know and I'll add hem to the list.

[Z8-NL]

I only weighed my front rim/tire. M6 rim plus PS2 and weight was 24.2k
If I get rear rim/tire off I will weigh that as well.

Off course the brembo kit weighs a lot less then stock as well

thanks
Klaus

[gutMD]

My E60 M5 19" Style 166 wheels arrived today.
Stats as follows. (Lighter than I thought they would be)

Front: 19 x 8.5, ET 12mm, 26 lbs
Rears: 19 x 9.5, ET 28mm, 29 lbs

Having Continental Sport Contact 2 mounted and will weigh again when complete and update post.

Weights: rims + tires

Front: 255/40/19, 53 lbs
Rears: 285/35/19, 59.5 lbs.

[Z8doc]

Are you going to need hub centric spacers for the front -- 12 mm offset -- in order to bring the wheel/tire combo back to the same overall position as the OEM wheel/tire setup? The Rear will probably be Ok but will be 16 mm overall more narrow of a stance compared to the OEM -- which I guess would give you less(?) oversteer potentially? GM-- care to weigh in on this question?

[gutMD]

Based on my calculations the rear stance will be entirely unchanged without need for spacers. The front wheels will protrude 14mm giving the front an overall wider and hopefully more aggressive stance, again without need for spacers.

[jawz]

Just put new PS2s on Alpina rims.
FWIW - Here are the weight details:

Alpina Rims:
Front - 31.6 lbs
Rear - 32.5 lbs

MPS 2:
Front (255/35) - 25.6 lbs
Rear (285/30) - 26.2 lbs

This makes a grand total of:
Front: 57.2 lbs each
Rear: 58.7 lbs each

Do these figures square to what others have found? (Just wondering about the accuracy of the weight scale used.)

[Norcal]

Doesn't look like PS2s come in 295/30/20 for the rears... Pirelli might be the best option

[ZMates]

Dinan wheels/PS2 tires

.........tires...........weight
front:..275/35/18..20.8kgs (45.8lbs)
rear:...285/35/18..21.1kgs (46.5lbs)